The present embodiments relate to coherent combinations of received ultrasound signals. In particular, adaptive line synthesis is provided for ultrasound.
Commercial ultrasound images are conventionally formed by focused array processing of pulse-echo events. For focusing, constructive interference of the array element signals is assumed to only occur in the case of echoes that were scattered or reflected directly from current desired point of focus, while echoes from any other path will destructively interfere. In practice, the quality of an ultrasound images may be degraded by many factors including side and grating lobes, acoustic aberration, deviation of the speed of sound from assumption, multiple reflection paths, probe or subject motion, inadequate array sampling, or even simply the presence of very strong off-axis scatters in the field.
To address acoustic clutter and aberration, many adaptive beamforming methods have been proposed, such as coherence factor (CF), generalized coherence factor (GCF), phase coherence imaging (PCI), Weiner filtering, minimum variance (MV) beamformation, and short-lag spatial coherence imaging (SLSC). These methods generally require raw acoustic data before beamformation (i.e., channel data). Processing based on channel data may be computationally expensive and storage demanding.
Separately, retrospective transmit focus synthesis is used to combine multiple interrogations of the same image point after beamformation to improve quality of transmit focus away from a physical transmit focus location. The summation of such signals is practically very different from conventional array beamforming. However, synthesis and beamforming are governed by very similar physical principals.